Résumé
Seven selected homozygous transgenic lines of two European commercial cultivars of rice (Ariete and Senia) and expressing the cry1B or the cry1Aa Bt-endotoxin gene under the control of the promoter of either the constitutive ubi1 gene or the wound-inducible mpi gene from maize, were field evaluated during the 2001 and 2002 summer crop seasons in the Delta Del Ebre, Spain. Stable, high level, insecticidal protein accumulation, was generally observed in root, leaf and seed tissues of field-grown plants harbouring the cry1B gene (lines 64.1, 33.1, 98.1 and 3.4) or the cry1Aa gene (lines 05.1 and 19.14) under the control of the maize ubiquitin promoter. Conversely, no toxin was detected in comparable, unwounded tissues of the mpi-cry1B 9.1 line indicating that natural environmental stresses did not induce the activity of the wound-inducible promoter. Natural and artificial infestations of the striped stem borer (Chilo supresssalis) revealed, upon observations of damage and dissection of tillers, a range of protection among the transgenic lines and the parental control lines, treated or not with chemical insecticides, which was consistent with the field level of accumulation of the toxins. Ariete Ubi-cry1B line 3.4 and Senia Ubi-cry1Aa line 05.1, were found to exhibit a stable and full protection against SSB attacks, comparable to that afforded by spraying of chemical insecticides on control plants. No dramatic change in morphology or performance was generally observed among the Bt lines compared to their conventional counterparts except in two lines which were those accumulating the Cry1Aa toxin. This work was suppported by the ERRI project from the European Community (Engineering Rice for Resistance to Insects. FAIR CT 97-3761). (Texte intégral)